Building the new common securitization platform for Fannie Mae and Freddie Mac may be the easy part. Plugging in the two government-sponsored enterprises is another story. Through the end of last year, the two GSEs had spent about $65 million to build the CSP, according to a report by the Inspector General of the Federal Housing Finance Agency. The IG estimated that Fannie and Freddie this year are spending about $6 million a month to continue that work. In fact, neither the GSEs nor the FHFA have yet come up...